This invention relates to a method of using 17.alpha.-dihydroequilenin to lower cholesterol and blood lipid levels and for preventing hypercholesterolemia hyperlipidemia, cardiovascular disease (CVD), atherosclerosis, and peripheral vascular disease.
Coronary artery disease, the primary form of CVD, is the major cause of death in the United States today, responsible for over 550,000 deaths per year. Cerebrovascular disease is the third leading cause of death in the United States. The etiology of both coronary artery and cerebrovascular diseases is attributed to atherosclerosis. Through its clinical manifestations, atherosclerosis is the major cause of the more than one million heart attacks and approximately 400,000 strokes that occur each year. In addition to the high morbidity and mortality associated with atherosclerosis, it has been estimated that atherosclerosis has cost the United States' economy over $80 billion each year in lost wages, lost productivity, and medical care costs Levy, R., Am. Heart J. 110:1116 (1985)!. A substantial body of evidence has established a causal relationship between hypercholesterolemia and premature atherosclerosis; the higher the levels of plasma cholesterol, the greater the risk of subsequent heart attack. Steinberg, D., JAMA 264:3047 (1991); Lipid Research Clinics Program, JAMA 251:351 (1984); Rifkind, B., Am. J. Cardiol. 54: 30C (1984)!.
In the chain of events leading to atherosclerosis, it is believed that the initiating event is the formation of "fatty streaks" in carotid, coronary, and cerebral arteries, and in the aorta. These lesions comprise of fatty deposits of cholesterol and cholesteryl ester that are found principally within the smooth muscle cells and macrophages of the intimal layer Ross, R., New Eng. J. Med. 295:369 (1977)!. The migration and proliferation of vascular smooth muscle cells play a crucial role in the pathogenesis of atherosclerosis following the initial deposition of lipid. Under normal circumstances, the cells of the arterial wall can be looked at as being under stringent negative control and in a quiescent non-proliferating state, probably the consequence of contact with their specialized extracellular matrix. Desquamation or injury of the endothelium, resulting in exposure of and possible disruption of the integrity of the extracellular matrix surrounding the cells, leads to 1) recruitment of circulating monocytes and their differentiation to macrophages, 2) accumulation of lipid in macrophages and smooth muscle cells Ross, R., New Eng. J. Med. 314:488 (1986)!, 3) a shift in smooth muscle phenotype from a quiescent, contractile state to a migrating, proliferative form Manderson, J. A., Arterio 9:289 (1989)!, 4) eventual migration of transformed smooth muscle cells from the medial layer to the sub-lesion intimal layer Clowes, A. W., Circ. Res. 56:139 (1985)! and 5) subsequent massive proliferation of the intimal smooth muscle layer resulting in arterial luminal blockage Clowes, A. W., J. Cardiovas. Pharm. 14 (Suppl 6): S12 (1989)!.
Several risk factors have been identified in individuals who develop atherosclerosis. It can be inferred that persons with at least one risk factor will be at greater risk of developing atherosclerosis than persons with no risk factors. Persons with multiple risk factors are even more susceptible. The risk factors include hyperlipidemia (hypercholesterolemia and/or hypertriglyceridemia), hyperglycemia, diabetes, hypertension, obesity, cigarette smoking, familial hyperlipoproteinemia, and aging. Of these factors, it is well established that elevated serum cholesterol levels is the one of the most important contributing factors leading to the development or progression of atherosclerosis.
Peri- and post-menopausal women are one particular group of aging persons at risk for developing coronary heart disease. Since the 1950s, it has been observed that premenopausal women are protected from coronary heart disease. These observations prompted several animal studies which demonstrated that the administration of estrogens to animals fed a high fat diet prevented dietary-induced coronary atherosclerosis. Barrett-Connor, E., JAMA 265:(1991)!. One of the mechanisms by which estrogen is thought to be protective against atherosclerotic coronary heart disease is by lowering total plasma cholesterol (TPC) through induction of increased catabolism and excretion of low density lipoprotein (LDL) particles into bile by the liver. This increased LDL catabolism and excretion may be a result of an estrogen dependent increase in low density lipoprotein receptors in the liver, as has been demonstrated in rats given large pharmacologic doses of 17.alpha.-ethinyl estradiol. Chao, Y-S., J. Biol. Chem. 254:11360 (1979); Kovanen, P. T., J. Biol. Chem. 254:11367 (1979); Windler E. E. T. , J. Biol. Chem., 255:10464 (1980)!. Women who receive postmenopausal estrogen replacement therapy (ERT) have been shown to benefit from a fifty to seventy percent reduction in risk from atherosclerotic related coronary heart disease. Stampfer, M. L., N. Engl. J. Med. 313:1044 (1985)!. The mortality from CVD is 63% lower and the rate of mortality from myocardial infarction is between 2.3 and 2.7 times lower in estrogen-treated women compared with untreated climacteric women.
While the benefits of ERT in postmenopausal women are substantial, an association has been established between the use of unopposed ERT (estrogen therapy without concomitant progestin administration) and endometrial hyperplasia, thereby increasing the risk of endometrial carcinoma. Utian, W. H., Obstet. Gynecol. Surv. 32:193 (1977); ACOG Technical Bulletin 93:1 (1986); Hammond, C. B., Fertil. Steril. 37:5 (1982); Whitehead, M. I., Am. J. Obstet. Gynecol. 142:791 (1982); Gambrell, R. D., South Med. J. 71:1280 (1978); McDonald T. W., Am. J. Obstet. Gynecol. 127:572 (1977)!. To reduce or entirely eliminate the risk of endometrial adenocarcinoma resulting from ERT while maintaining the benefits of ERT, it has been shown that progestins can be administered concomitant with the estrogen during the last 10-14 days of each estrogen cycle. Whitehead, M. I., J. R. Soc. Med. 72:322 (1979); Whitehead, M. I., Semin. Reprod. Endocrin. 1:41 (1983); Barrett-Connor, E., Annu. Rev. Med. 43:239 (1992)!.
The isolation of 17.alpha.-dihydroequilenin from pregnant mare's urine was reported in 1956. Glen, W. L., Nature 177:753 (1956)!. 17.alpha.-Dihydroequilenin sulfate is a 1% by weight component of PREMARIN.RTM. conjugated estrogens (PREMARIN is a Registered Trademark of Wyeth-Ayerst), a drug commonly prescribed as ERT in postmenopausal women. There have been several reports of the relative estrogenicity of various estrogens to determine if they have differential effects on menopausal vasomotor symptoms, urinary gonadotropin levels, plasma lipid and lipoprotein metabolism and hepatic globulin synthesis compared to uterine response. Two studies showed that 17.alpha.-dihydroequilenin had essentially no stimulatory effect on uterine weight or maturation of vaginal cytology in the rat model and did not suppress urinary gonadotropins in postmenopausal women. Estrogenic activity was nil to minimal. Howard, et al., Arch Int. Med. 128:229 (1971); Stern, Maturitas 4:333 (1982). Neither study suggested the use of 17.alpha.-dihydroequilenin in lowering cholesterol.